The invention relates to a double link level luffing crane comprising a base, jib including a strut member hinged to the base, a backstay member hinged to the base and a jib head member, drive means for luffing the crane in and out, hoisting equipment, a drivers cab mounted on a cab link, and means for pivoting the cab link during luffing of the crane so that the drivers cab moves along a substantially horizontal path.
Such a crane is known from German Auslegeschrift No. 1,161,669.
In luffing a double link level luffing crane the pulley block at the free end of the jib head member will move along a substantially horiztonal path. This means that the load also moves along a substantially horizontal path and the free length of the cable of the hoisting equipment remains the same. As a consequence higher turning and luffing speeds are possible. An important advantage of the double link level luffing crane is that the length of the cable underneath the pulley block is rather small, so that the positioning of the grab is easier and the grab is less likely to swing during positioning.
In addition the crane according to said German Auslegeschrift is advantageous as the crane drivers cab will move along a substantially horizontal path during the luffing movement and the driver will be in a good position to observe loading and unloading. However, the height position of the cab is fixed. In the embodiment shown this position is rather low and as a consequence it is unsuitable for loading and unloading of a rather big ship. If the fixed height position of the cab is chosen to be much higher, the crane driver in loading or unloading a rather small ship would be at such an elevation that his sight on the ship and especially on the load in the hold would be poor.
The object of the invention is to give the cab of a crane such a position that the crane driver may have an optimal sight on the loading and unloading by selecting the height of the cab.